The present invention relates to a hydraulic control unit for a motor-vehicle braking system, in particular for a motor-vehicle braking system with a pump delivering a hydraulic fluid under pressure, said pump being capable of being controlled by an electronic control unit and supplying the hydraulic fluid for at least one braking device which is coupled to a wheel of the vehicle, and with a first reservoir for pressureless hydraulic fluid, which is assigned to the pump on the input side.
In the state of the art, pressure accumulators by way of developments of a second reservoir are known which are designed as gas-piston accumulators, as gas-diaphragm accumulators or as multilayer gas-diaphragm accumulators, or as spring-piston accumulators. In this connection the physical size of the respective pressure accumulators varies considerably for the same useful volume. Furthermore, for pressure accumulators with gas filling there are problems with respect to the temperature dependence and the imperviousness in long-term behaviour. Further disadvantages in the case of multilayer gas-diaphragm accumulators are the considerable weight and the high costs. In the case of spring-piston accumulators there is the problem of wear and tear of the seal between the cylinder and the moving piston. All these problems limit the operating life of the pressure accumulators.
In the case of the electrohydraulic braking systems that are known in the state of the art, use is made of standard commercial gas accumulators or diaphragm accumulators which are screwed to an outer side of the hydraulic unit. As a result, the hydraulic unit becomes unshapely, so that problems as regards installation space arise in not uncritical manner.
A control device for brake fluid with a pump delivering hydraulic fluid under pressure is known from JP-09086362 A. The pump is capable of being driven by a motor, and a first reservoir for pressureless hydraulic fluid is assigned to said pump on the input side. A second reservoir for hydraulic fluid under pressure is assigned to the pump on the output side. In a drawing pertaining to JP-09086362 A the pump and the first and second reservoirs and, in particular, also the motor are combined so as to form an operating block. There is no indication in JP-09086362 A that the aforementioned operating block is to be equated to a casing. In known motor-vehicle braking systems the motor driving the pump has its own motor casing which, for the most part, is produced from synthetic material. This motor casing is attached to a pump casing which, as a rule, is manufactured from a metal alloy. Since the motor and the pump already have two individual casings, for a person skilled in the art of motor-vehicle braking technology it is eccentric to equate the operating block to a casing.
From the printed publication by Leichner, K. H.: xe2x80x9cFahrzeuggerechte Speichersysteme und ihre Einsatzbedingungenxe2x80x9d, in O+P xc3x96lhydraulik und Pneumatik, Vol. 36, 1992, No. 8, pp 498-501, a metal-bellows accumulator subject to gas preloading is described that is less capable of being employed in the motor-vehicle industry. In this printed publication, the practical implementation of such metal-bellows accumulator is assessed quite severely in comparison with diaphragm accumulators as they exist at the present time.
From U.S. Pat. No. 4,858,898 a pressure accumulator for a vehicle is known which is provided, in particular, as a spring device. With this pressure accumulator, hydraulic fluid is conveyed to a spring-loaded bellows made of metal which encloses a gas chamber. In the process the gas enclosed within the gas chamber is compressed and constitutes a counterforce for the hydraulic fluid.
The object underlying the invention is to develop further the hydraulic control unit mentioned in the introduction in such a way that these disadvantages are avoided.
In order to achieve this object, the pump, the first reservoir and the second reservoir are arranged in a common casing.
In this way, on the one hand a considerable saving of weight is obtained, since a separate outer wall of the pressure accumulator becomes unnecessary. On the other hand, the integration of two functions (storage of potential energy and enclosure of the fluid) in one structural part enables a considerable simplification of the overall arrangement. Furthermore, moving seals, which can wear out by reason of friction, are avoided. Since conduction paths are dispensed with or are considerably shortened, a reduction in weight and a reduction of installation effort are also achieved.
By virtue of the integration of the first reservoir and the associated omission of the return and suction line, there is the advantage furthermore that the induction path leading to the pump can be designed not only to be considerably shorter but also, above all, to have a considerably larger induction cross-section, resulting in an improved suction behaviour of the pump, particularly at low temperatures, which contributes to enhancing the performance of the electrohydraulic braking system.
The second reservoir is preferably a hydraulic pressure accumulator, into which the hydraulic fluid is capable of being conveyed by the pump contrary to the force of a spring arrangement, whereby at least a first part of the spring arrangement is formed by a corrugated bellows, preferably made of metal.
Astonishingly, by virtue of the configuration according to the invention it is possible to obtain a space requirement that is barely greater than or even less than the space requirement of a traditional gas-pressure accumulator.
Nevertheless, the pressure accumulator according to the invention is not temperature-dependent or is barely temperature-dependent and, by reason of the absence of moving seals, has no wear problems.
According to the invention, one wall of the hydraulic pressure accumulator is formed at least partially by a recess in the casing. In this connection a considerable amount of material and weight is eliminated in comparison with the state of the art.
In this case the corrugated bellows is connected at a first end to a cover, which seals the recess in the casing, and is connected at a second end to a base.
Hence the corrugated bellows divides the recess in the casing into two regions, of which a first (inner or outer) region can be filled with gas and a second (outer or inner) region forms the second reservoir for hydraulic fluid under pressure. The included gas assists the spring action of the spring arrangement.
An advantageous further development provides that the corrugated bellows divides the recess in the casing into two regions, of which a first (inner or outer) region forms the first reservoir for pressureless hydraulic fluid and a second (outer or inner) region forms the second reservoir for hydraulic fluid under pressure. This measure achieves an especially high utilisation of space.
In a preferred embodiment of the invention a first aperture extending into the first region is provided which connects said first region to an overflow vessel.
In addition, a second aperture extending into the first region is arranged in the cover, which connects said first region to the input side of the pump.
Finally, a third aperture extending into the second region is arranged in the wall of the recess, which connects said second region to the output side of the pump.
A controllable valve arrangement is preferably arranged between the third aperture extending into the second region and the output side of the pump. Furthermore, yet other valve arrangements may also be integrated into the control unit.
In addition, a hydraulic-fluid line is arranged between the pressureless region and the region under pressure, preferably in the base, in which a pressure-relief valve is located which at a predetermined first pressure level in the region under pressure establishes a fluid-conducting connection from the region under pressure to the pressureless region and at a predetermined second pressure level in the region under pressure interrupts the fluid-conducting connection from the region under pressure to the pressureless region. Hence the pump delivers in the event of excessive pressure in the circuit.
With a view to increasing the achievable pressure level, a second part of the spring arrangement is arranged preferably parallel to the first part of the spring arrangement, which assists the action of the first part of the spring arrangement.
In a first embodiment of the invention the second part of the spring arrangement is a helical spring taking the form of a compression spring which is arranged between the base and the cover.
As an alternative to this, the second part of the spring arrangement may be a helical spring taking the form of a tension spring which is arranged between the base and the wall of the recess.
It is to be understood that the arrangement of the helical spring inside or outside the corrugated bellows as well as its design as a tension spring or compression spring may also be permuted with respect to the alternatives described above.
In both cases the maximal expansion of the reservoir for hydraulic fluid under pressure is limited by a stop member.
The pump is coupled by a transmission to an electric motor which is controlled by the electronic control unit (ECU).
Although the hydraulic control unit described above has been described for a motor-vehicle braking system, to a person skilled in the art it is also readily apparent that the hydraulic control unit according to the invention can also be employed for other purposes. For instance, a subassembly consisting of the cover, the base, the spring-loaded corrugated bellows and/or the helical spring can be inserted into an appropriately shaped recess or bore in a casing, into which yet other components (e.g. valves or such like) may also be integrated but do not have to be.
In this case the casing may be formed as a moulding made of metal or synthetic material. In this connection the space that is formed by the cover, the corrugated bellows and the base may be either the reservoir for the pressurised hydraulic fluid or the space for the pressureless hydraulic fluid. This is dependent on the cabling and on the incoming and outgoing lines.